Conventionally, a fuel injection pump mounted on a large diesel engine is known in which timing and number of times of fuel injection is controlled corresponding to the driving state of the engine for improving fuel efficiency and reducing exhaust gas emission. In such a fuel injection pump, an electromagnetic spill valve is opened and closed at optional timing so as to perform accurate fuel injection.
In the electromagnetic spill valve, a spill valve body is opened and closed complicatedly and quickly corresponding to the driving state of the engine, whereby large impact and rubbing occur continuously. As a result, abrasion occurs in a seal surface and a valve seat, whereby the seal surface cannot sit closely on the valve seat and fuel leaks. Accordingly, for improving abrasion resistance of the seal surface and the valve seat, it is necessary to construct the spill valve body and the whole housing with material having high strength, whereby the manufacturing cost is increased.
Then, the art has been proposed in which material (surface) constructing one of a spill valve body (valve object) in which a seal surface (seat part) is formed and a housing (valve body) in which a valve seat (valve seat part) is formed is softer than material constructing the other thereof. According to this art, when abrasion occurs in the seal surface (seat part) or the valve seat (valve seat part), the one of the surfaces formed the softer material follows the shape of the other surface, whereby the seat part touches closely to the valve seat part and the leakage of fuel is reduced. The art shown in the Patent Literature 1 is an example of the above-mentioned art.
However, in such an art as shown in the Patent Literature 1, when the abrasion in the seat part and the valve seat part is advanced and the effect of reduction of fuel leakage by the softer material cannot be obtained, the whole electromagnetic spill valve must be exchanged for maintain the sealing characteristic of the electromagnetic spill valve. Namely, there is a problem in that construction members of the electromagnetic spill valve which do not need to be exchanged are exchanged simultaneously, whereby the maintenance cost which is not necessary essentially is caused.